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Hydrogen was prepared many years before it was recognized as a distinct
substance by Cavendish in 1766. It was named by Lavoisier. Hydrogen is the most abundant of all elements in the universe, and it is thought that the
heavier elements were, and still are, being built from hydrogen and helium. It has been estimated that hydrogen makes up more than 90% of all the
atoms or three quarters of the mass of the universe. It is found in the sun and most stars, and plays an important part in the proton-proton reaction and
carbon-nitrogen cycle, which accounts for the energy of the sun and stars. It is thought that hydrogen is a major component of the planet Jupiter and
that at some depth in the planet’s interior the pressure is so great that solid molecular hydrogen is converted into solid metallic hydrogen. In 1973, it
was reported that a group of Russian experimenters may have produced metallic hydrogen at a pressure of 2.8 Mbar. At the transition the density
changed from 1.08 to 1.3 g/cm3. Earlier, in 1972, a Livermore (California) group also reported on a similar experiment in which they observed a
pressure-volume point centered at 2 Mbar. It has been predicted that metallic hydrogen may be metastable; others have predicted it would be a
superconductor at room temperature. On earth, hydrogen occurs chiefly in combination with oxygen in water, but it is also present in organic matter
such as living plants, petroleum, coal, etc. It is present as the free element in the atmosphere, but only to the extent of less than 1 ppm by volume. It
is the lightest of all gases, and combines with other elements, sometimes explosively, to form compounds. Great quantities of hydrogen are required
commercially for the fixation of nitrogen from the air in the Haber ammonia process and for the hydrogenation of fats and oils. It is also used in large
quantities in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization. It is also used as a rocket fuel, for welding, for
production of hydrochloric acid, for the reduction of metallic ores, and for filling balloons. The lifting power of 1 ft3 of hydrogen gas is about 0.076
lb at 0°C, 760 mm pressure. Production of hydrogen in the U.S. alone now amounts to about 3 billion cubic feet per year. It is prepared by the action
of steam on heated carbon, by decomposition of certain hydrocarbons with heat, by the electrolysis of water, or by the displacement from acids by certain
metals. It is also produced by the action of sodium or potassium hydroxide on aluminum. Liquid hydrogen is important in cryogenics and in the study
of superconductivity, as its melting point is only a 20 degrees above absolute zero. The ordinary isotope of hydrogen, H, is known as protium. In 1932,
Urey announced the discovery of a stable isotope, deuterium (2H or D) with an atomic weight of 2. Deuterium is present in natural hydrogen to the
extent of 0.015%. Two years later an unstable isotope, tritium (H), with an atomic weight of 3 was discovered. Tritium has a half-life of about 12.5
years. Tritium atoms are also present in hydrogen but in much smaller proportion. Tritium is readily produced in nuclear reactors and is used in the
production of the hydrogen bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer. Deuterium gas is readily available,
without permit, at about $1/L. Heavy water, deuterium oxide (d2O), which is used as a moderator to slow down neutrons, is available without permit
at a cost of 6c to $1/g, depending on quantity and purity. Quite apart from isotopes, it has been shown that hydrogen gas under ordinary conditions
is a mixture of two kinds of molecules, known as ortho- and para-hydrogen, which differ from one another by the spins of their electrons and nuclei.
Normal hydrogen at room temperature contains 25% of the para form and 75% of the ortho form. The ortho form cannot be prepared in the pure state.
Since the two forms differ in energy, the physical properties also differ. The melting and boiling points of parahydrogen are about 0.1°C lower than
those of normal hydrogen. Consideration is being given to an entire economy based on solar- and nuclear-generated hydrogen. Located in remote
regions, power plants would electrolyze sea water; the hydrogen produced would travel to distant cities by pipelines. Pollution-free hydrogen could
replace natural gas, gasoline, etc., and could serve as a reducing agent in metallurgy, chemical processing, refining, etc. It could also be used to convert
trash into methane and ethylene. Public acceptance, high capital investment, and the high present cost of hydrogen with respect to present fuels are
but a few of the problems facing establishment of such an economy. 1

•&nbsp"The most important industrial uses of hydrogen are in catalytic hydrogenation processes. In the Haber process, nitrogen and hydrogen are combined to form ammonia. Methanol is produced by the reaction of carbon monoxide and hydrogen. Unsaturated vegetable oils, such as cottonseed oil, are hydrogenated to saturated, solid fats." 2
•&nbsp"Hydrogen gas is in many respects an ideal nonpolluting fuel as well as an important reducing agent in the food and petrochemical industries. There has been much discussion of an environmentally benign, hydrogen-based economy for the future, but extraction of hydrogen from water without recourse to the fossil fuels it is intended to replace presents a formidable challenege to chemists and chemical engineers." 3
•&nbsp"Approximately 40% of the hydrogen produced commercially is used to manufacture ammonia, and about the same amount is used in petroleum refining. But the future may hold an even greater role for hydrogen as a fuel.

Liquid hydrogen, H2, is a favorite rocket fuel. Burning it produces more heat per gram than any other fuel. In its gaseous form, hydrogen may become the favorite fuel of the twenty-first century. When hydrogen burns in air, the product is simply water. Therefore, the burning of hydrogen rather than fossil fuels (natural gas, petroleum, and coal) has important advantages.

Controlling carbon dioxide emissions into the atmosphere is a difficult challenge, but the answer might lie in the conversion to a hydrogen energy economy. In a hydrogen economy, hydrogen would become a major energy carrier. Automobiles, for example, could be modified to burn hydrogen. Hydrogen is not a primary energy source, however. It is a convenient and nonpolluting fuel, but it would have to be obtained from other energy sources." 4

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